THE LA FOLIA MAGNETOSTATIC RIBBON LOUDSPEAKER DEVELOPMENT PROJECTTips and tricks© 1998-2004. All rights reserved on text, photos, diagrammes, etc, unless otherwise stated. |
| Here I will now include some tips and tricks I forgot to place on the original docs here on the site. I have felt compelled to do so due to a few mails that I have received from friends around the world. Here we go: I know this has been one of the very hard parts of this project, how the h... do I cut a perfect strip of aluminium foil that, to make things harder, is very fragile and then stick it on the membrane in an easy way? Well, this is not my own original idea but I used it with very good success while building my model. In Chile there is a special type of paper that is used for chocolate, it is a waxed paper that on one side has a very thin aluminium foil, much thinner than the foils used for food. I Chile the problem was to buy a sheet large enough to include the complete design in one piece. I had to travel to Santiago and then go to a packaging industry, there among the trash I found some 10-15 meters of the stuff, that I now have for future projects. The guy there could not believe I would later use it to build a loudspeaker, he gave me his address so I could send him a picture... never did... but if he has access to Internet he might find this site one day... In Denmark this paper is used to package sandwiches (well the Danish style sandwiches smórrebród) and can be bought in the right width at a normal supermarket (lucky them). If you live elsewhere you must see where you can find it, good luck, but it is very much worth the effort. What do you do then: You design your membrane by drawing on the foil, then you use two very sharp blades stuck together, separated by a small coin or equivalent, careful to align them well. These blades you will use to cut the covering aluminium without cutting the underlying paper, so be careful and delicate. This way you will obtain the design by removing (very very carefully) the thin strip created by the blades. And you will have the complete design of the membrane placed on paper, with the strips much closer and perfect than you ever could do by sticking aluminium on the plastic membrane. Now you stretch the plastic membrane on a table and place the adhesive on the surfaces and stick the aluminium side on the plastic membrane, careful when you unwrinkle the membrane when it is wet it can easily rip, a horrible thing that happened to me... Now it's a matter of taking off the paper without taking the aluminium off... and that's where the wax comes into the show, you use a hairdrier in the hot setting and heat the paper until the wax melts and you are able to pull it off from the aluminium! This is delicate too. So this is an easy method and I like it much more than what I believe is a very tedious method, the alum strip of conductor. Now another interesting subject is the membrane material. In the first model I used a rather thick Mylar membrane my brother had for windsurf sails around 50 um. (micrometers) and later I used a sticker material with golden colour of half the width. In the second model I used what the original design recommended, two slit oven bags. I did not test them out before and the surprise was that the speakers became gigantic hygrometers, I was able to predict bad weather by looking at my speakers, they would go limp and stretch out on sunny and dry days... :-( This my recommendation is that you test the membrane material's response to humidity before you use it. Take a piece of the material, stretch it out over a frame and go into the bathroom and turn on the hot water and see if it goes limp. If it does change the membrane material. I have since bought a roll of 12 um. (micrometers) Mylar for the next model, Mylar is a very resistant material and considering the good results I obtained in the first model I think this will help considerably with the next model. Here is an interesting subject that can be easily overcome by using a very good, effective and easy to use glue made by the 3M company, free advertising I am doing for them, it's a spray glue that comes in a black can, Super 77. This is the solution, follow the instructions given and try to use it sparingly and uniformly, practice on useless surfaces before the real stuff. Practical tips
OK, that seems to be all for now, if I remember anything more I will add it. Hope this can come in handy for you all. |
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Once
you have designed the membrane you'll notice there are sections
that connect the different portions of the conductors that are between
the magnet poles, these are not contributing to the membrane movement,
and therefore do not need to be between the magnetic poles, a way
to have them do no harm by adding to the membrane dead weight is
to place them outside the stretched portion of the membrane, that
is on the MDF plate. This way the real portion that is doing the
work is suspended between the magnets and the dead weight is lowered
helpin the efficiency of the system, at least a bit.